Process fob the continuous ex



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Patented Jan. 10, 1939 2,143,310

UNITED STATES PATENT OFFICE PROCESS FOR THE CONTINUOUS EX- TRACTION OF ALUMINUM OXIDE FROM BAUXITE Wilhelm Fulda, Lautawerk, Lausitz, and Rudolf Wittig, Grevcnbroich, Niederrhein, Germany No Drawing. Application February 3, 1936, Se-

rial No. 62,224. In Germany February 2, 1935 9 Claims. (UL 23-143) (Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G.

The hitherto employed Bayer process for mantraction temperature. The aluminum hydrate is ufacturing pure aluminum oxide from aluminumremoved by stirring from the liquor leaving the containing materials, depends upon the extractowers in the ordinary way. tion of the aluminum oxide from bauxite by The removal of extraction residues from the means of soda liquor. The existing practice is towers may for example be effected by running 6 to submit the bauxite in batches, after roasting water through them. in a finely divided state, to extraction by 'stir- A process is known in which bauxite is subring it in an autoclave with soda. liquor of above mitted to continuous extraction by stirred alumi- 40 B. The mixture must then, before filtering nate liquor of 20-22 B. at temperatures above 0 off the iron residues in a filter press, be cooled 190 C. and at hig Pressures p 110 109 atmOS- and diluted to about 25? B. The filtration of pheres). The new process has the following imthese iron residues requires a great expenditure portant advantages over this known process:-

of filter material, as peptization of the iron par- 1. It is not necessary to grind the bauxite to ticles occurs owing to the stirring in the autoa very fi ate o Subd vision. sieve. The aluminum hydrate is then separated e filtration 0 e St n y bau tB inby stirring the clear aluminate liquor which convolves no difiiculties and little if any filtration stitutes the filtrate. For a fresh extraction the Costs.

stirred aluminate liquor must then be concen- N0 P i ul rl high pressures r t mperatrated by evaporation up to above 49 B. tures are necessary, which involve heavy radia- This and the extraction of the material in seption losses and are very cu t to Work with 29 arate batches, instead of continuously, necessiin practice.

tates a large consumption of heat. Further the The following iS an example of how the process filtration involves heavy costs owing to the use according to the invention may be carried into of large quantities of textile materials. P ct e.

These disadvantages of the Bayer process are A pressure resisting iron tower with a sieve removed by the present invention. bottom of porous carbon plates was filled with It has been found that bauxite can be sub- 00 kg. of calcined bauxite, of a ra n Size of jected easily to complete extraction in the staabout 5 mm. The tower was well insulated. tionary condition by causing hot soda. liquor and F om supp y tank, ontaining stirred aluminate especially a. stirred aluminate liquor (i. e. all quors C n e t a ed to about 20 Be. and at a 30 uminate liquor irom which aluminum hydrate temperature of 179 (corresponding to a, pressure has been removed by stirring as described above) of 9 atmospheres). the liquor flowed continuously to flow through it at a high temperature and through the tower filled with bauxite. Behind under pressure. The bauxite is introduced in a, the tower was a reducing valv which egulated coarse state of subdivision into towers, the botthe speed of flow of the liquor. The liquor flowtoms of which are advantageously constructed ing from the tower had a molecular constituas sieve plates, 1. e. by making them of porous tion of Al2O::Na20=1:1.8, and was only slightly carbon. The stirred aluminate liquor of about darkened by iron oxide which was readily re- 22 B., if desired with addition of the washing movable by a suitable filter. The liquor from water of the separated aluminum hydrate or the tower was sent in countercurrent through after slight evaporation to a concentration of a heat exchanger, through which the stirred about 28 131%., is pumped into a preheater, there a umi m liquor was p p on s ay r m heated to about 180 C. and then passed through th ank to the tower.

a tower filled with bauxite or t h one or The washed extraction residue gave an analysis more such towers in series. The size of the a yield of 93% aluminum Oxide- The Switching 5 towers and the quantity of bauxite are prefera over from a fully extracted tower to a tower so selected that the liquor flowing from the last freshly filled with bauxite was easily one y tower is of the molecular constitution g al g v the p p C n c s rom the Equal success was obtained when the stirred The temperature of the liquor in the towers is m m t liquor had concentration of maintained at at least 160-180" C. by means of 192 B. heating jackets. The liquor leaving the towers What; we claim is; is s n th o a heat h n r, wh h r i e 1. A process for the continuous extraction of the entering stirred alumlnate liquor to the exl minu oxide from bauxite which comprises contacting a continuous flow of heated caustic soda liquor under pressure with a stationary charge of coarse bauxite, eifecting thereby a practically complete dissolution of the aluminum oxide contained in the bauxite and treating the resulting sodium aluminate solution for the precipitation and recovery of the aluminum oxide.

2. In a process for the continuous extraction of aluminum oxide from bauxite the step of continuously flowing a heated caustic soda liquor under pressure through a stationary column of coarse bauxite.

3. A process for the continuous extraction of aluminum oxide from bauxite which comprises contacting a continuous flow of heated caustic soda liquor under pressure with a stationary charge of coarse bauxite, effecting thereby a practically complete dissolution of the aluminum oxide contained in the bauxite, treating the resulting sodium aluminate solution for the precipitation and recovery of the aluminum oxide, and recirculating the aluminum oxide freed solution for further decomposition of the bauxite.

4. A process for the continuous extraction of aluminum oxide from bauxite which comprises contacting a continuous flow of heated caustic soda liquor under pressure with a stationary charge of comparatively coarse bauxite to effect an aluminate solution practically equal to the molecular constitution AliOu:Na,O=1:1.8, precipitating from this solution the aluminum oxide, separating the same and recirculating the aluminum oxide freed solution for further extraction of the bauxite.

5. In a process according to claim 1, the step of bringing the aluminum oxide freed solution to a concentration of about 20-28 Be. and re circulating the same for renewed extraction.

6. A process according to claim 1, characterized by maintaining a temperature of about C. during the decomposition of the bauxite.

7. A process according to claim 3, characterized by maintaining a temperature of about 160- 180 C. during the decomposition of the bauxite.

8. A process according to claim 1, consisting in heating the caustic soda liquor by flowing the same in countercurrent to the hot solution produced by the dissolution of the bauxite.

9. A process according to claim 3, consisting in heating the recirculated aluminum oxide freed solution by flowing the same in countercurrent to the hot solution produced by the decomposition of the bauxite.

WILHELM F'ULDA. RUDOLF WITTIG. 

